A floor of an automobile vehicle body (hereinafter, simply referred to as “floor”) is not only primary responsible for torsional rigidity and bending rigidity of a vehicle body when the vehicle travels, but also responsible for transfer of an impact load when a crash occurs, and further, it exerts a large influence on a weight of the automobile vehicle body, so that it is required to have antinomy characteristics such as high rigidity and light weight. The floor includes planar panels (for example, a dash panel, a front floor panel, a rear floor panel, and so on) which are welded to be jointed with each other, long cross members (for example, a floor cross member, a seat cross member, and so on) having approximately hat-shaped cross sections which are fixed to be disposed in a vehicle width direction of these planar panels by welding to enhance rigidity and strength of the floor, and long members (a side sill, a side member, and so on) having approximately hat-shaped cross sections which are fixed to be disposed in a forward and rearward direction of vehicle body to enhance the rigidity and the strength of the floor. Out of the above, the cross members are normally jointed to other members such as, for example, a tunnel part of the front floor panel and the side sill by using outward flanges formed at both end parts in a longitudinal direction thereof as joint margins.
FIG. 8A to FIG. 8C are explanatory views illustrating a floor cross member 1 being a typical example of the cross members, in which FIG. 8A is a perspective view of the floor cross member 1, FIG. 8B is a VIII arrow view in FIG. 8A, and FIG. 8C is an explanatory view illustrating a portion surrounded by a circular dotted line in FIG. 8B, in an enlarged manner.
For example, a front floor panel 2 generally includes a tunnel part (illustration is omitted) jointed to an upper surface (a surface at an interior side) of the front floor panel 2 and placed at approximately a center in a width direction of the front floor panel 2, and side sills 3 spot-welded at both side parts in the width direction of the front floor panel 2. The floor cross member 1 is jointed to the tunnel part and the side sills 3 by the spot welding or the like using outward flanges 4 formed at both end parts in a longitudinal direction thereof as joint margins, thereby improving rigidity of the floor and a load transfer characteristic when an impact load is applied.
FIG. 9A and FIG. 9B are explanatory views illustrating an outline of a conventional press forming method of the floor cross member 1, in which a region of an end part in a longitudinal direction of the member 1, in particular, is illustrated in an enlarged manner. FIG. 9A illustrates a case where the press forming is performed by drawing, and FIG. 9B illustrates a case where the press forming is performed by bend forming using an expanded blank 6.
The floor cross member 1 has been formed so far in a manner that an excessive material volume part 5a is formed at a forming material 5 through the press forming by the drawing as illustrated in FIG. 9A, the excessive material volume part 5a is cut along a cutting-line 5b, and a flange 5c is then raised, or the press forming by the bend forming is performed on the expanded blank 6 having an expanded blank shape as illustrated in FIG. 9B. Note that from a point of view of the improvement of material yield, the press forming by the bend forming is more preferable than the press forming by the drawing accompanied by the cutting of the excessive material volume part 5a. 
The floor cross member 1 is an important structural member which is responsible for the rigidity improvement of the automobile vehicle body and transfer of the impact load at a time of side surface crash (side impact). Accordingly, in recent years, a thinner and higher-tensile strength steel sheet, for example, a high-tensile strength steel sheet with a tensile strength of 390 MPa or more (a high tensile strength steel sheet or a high-ten) has been used as a material of the floor cross member 1, from a point of view of reduction in weight and improvement in crash safety. However, formability of the high-tensile strength steel sheet is not good, and therefore, it is a problem that flexibility of design of the floor cross member 1 is low.
This will be concretely described with reference to FIG. 8A to FIG. 8C.
It is desirable that the outward flange 4 at the end part in the longitudinal direction of the floor cross member 1 is continuously formed by including a part 4a along a ridge line part 1a, and has a certain degree of flange width, as indicated by a dotted line in FIG. 8C, in order to enhance jointing strength between the floor cross member 1 and the tunnel part of the front floor panel 2, the side sills 3, and to enhance the rigidity of the floor and the load transfer characteristic when the impact load is applied.
However, when the continuous outward flange 4 including the part 4a along the ridge line part 1a is tried to be formed through cold press forming, and the certain degree of flange width is tried to be obtained, basically, stretch flange fractures at an outer peripheral edge portion of the part 4a along the ridge line part 1a, and wrinkling at an end portion 1b in a longitudinal direction of the ridge line part 1a of the floor cross member 1 and at a position from a center portion to a vicinity of a root of the part 4a along the ridge line part 1a occur, which makes it difficult to obtain a desired shape. These forming failures are easy to occur as a strength of steel material used for the floor cross member 1 is higher, and in a shape with higher stretch flange rate at the forming of the part 4a along the ridge line part 1a (namely, for example, as a cross sectional wall angle θ in FIG. 8B or a rising angle α of an end part (refer to FIG. 1B) is steeper).
The floor cross member 1 tends to be high-strengthened to reduce the weight of the automobile vehicle body, so that the cold forming of the continuous outward flange 4 including the part 4a along the ridge line part 1a tends to be difficult to be enabled by the conventional press forming method. Accordingly, even if lowering of the rigidity in the vicinity of the joint part of the floor cross member 1 with the other member and the load transfer characteristic is accepted, due to restrictions on the press forming technology as stated above, it is the present situation in which the occurrence of forming failures has to be avoided by providing, to the parts 4a along the ridge line parts 1a of the outward flange 4 of the floor cross member 1 made of the high-tensile strength steel sheet, cutouts 4b each of which is deep to some extent that it reaches the end portion 1b in the longitudinal direction of the ridge line part 1a, as illustrated in FIG. 8A and FIG. 8B.
Patent Literatures 1 to 4 disclose the inventions in which the improvement in the shape freezing property after the forming is realized by devising a pad of a forming tool, in order to manufacture a press-formed member having a hat-shaped cross section. Further, Patent Literature 5 discloses the invention in which a movable punch of a forming tool is devised to perform press forming on a panel component.